I think Ti alloy can be welded using TIG equipment without using an Argon filled enclosure. Bicycle frames are routinely welded up that way. ...........The interior of the tubes are purged of air and fed pressurized Argon through plugs in the tube ends.

desmo- Yes, some people do TIG weld titanium tubular structures like bicycle frames or exhaust headers using inert gas purge on the backside of the weld joint, and relying on the nozzle gas flow to shield the top side of the joint. But this is different situation than welding the joints of gearbox housing components (like those shown in Tony Matthews' illustration) where the backside of the weld joints cannot be sealed and purged. In these instances, manual TIG welding titanium usually requires a glove box.

Tony Matthews- Thanks for the reply.

As noted, DLS process can actually produce prototype titanium parts with fair metallurgical properties. However, wrought material weldments or HIP'd investment castings would give better properties. For a race team, the approach of using a weldment of machined parts is attractive because the work can all be done in-house, giving them control over schedule.

Investment cast titanium housing:

Lastly, here's a link to an extensive trade study done in 1975 by Sikorsky for a highly-loaded, fabricated main rotor gearbox housing on the CH-54 helicopter. Their conclusion was that the best option for weight, fatigue life and reliability was a welded truss structure made from Custom 455 stainless steel with bonded/riveted close-out panels. It's over 200 pages, but definitely worth a read.

Slider,
Great post, in particular that image of the investment-cast Ti-housing, thanks a lot!

A question there, that vertical joint intrigues me, how do you figure that is held together, just by those tiny radial screws,
or are there other means as well? It makes me wonder as it must be subjected to all sorts of loads?

Tony's drawing seems to have lost it's ability to be hot linked to here but you can open the image by copying the image url and opening it in a new tab. It's probably just me but I'm not seeing where the weld joins are in that illustration. The upper and lower panels I'm guessing. Pretty astonishing to consider that cast Ti box was pioneered by little Minardi!

Tony's drawing seems to have lost it's ability to be hot linked to here but you can open the image by copying the image url and opening it in a new tab. It's probably just me but I'm not seeing where the weld joins are in that illustration. The upper and lower panels I'm guessing. Pretty astonishing to consider that cast Ti box was pioneered by little Minardi!

I'm surprised it can't be seen, but there you go, an added air of mystery... For those that can see it, all parts forward of the vertical split on the diff housing, and all those behind it, were welded together, leaving two main fabricated units. I have photos, I will post.

This is a photograph I couldn't find, but suddenly appeared, as things do, after I had scanned and posted the others. It gives a good idea, in one shot, of most of the welds that go to make the complete box.

This is a photograph I couldn't find, but suddenly appeared, as things do, after I had scanned and posted the others. It gives a good idea, in one shot, of most of the welds that go to make the complete box.

That particular picture is actually interesting from one standpoint. If you look closely you can see several internal machined features (threaded holes, bores, etc.) that probably had to be machined into the parts before welding. So a welded construction allowed some things to be done that could not be done with other methods.

With something like a gearbox housing that requires a high degree of dimensional accuracy for features like bearing bores, etc., some finish machining after welding is probably mandatory. A post weld stress relief would also be a good idea. Titanium has a very high melting temperature and very low thermal conductivity. So a titanium structure with thin sections and that requires lots of fusion welding would naturally end up with lots of post weld distortion and internal strains. On the plus side, titanium alloys have excellent strength in the annealed condition. So a titanium weldment would only need a simple thermal stress relief and anneal cycle, with no quenching and the distortions that would result.